I think there is a common problem at the base of this, which is that the animations for entering a vehicle are just for show and you can start interacting with the vehicle almost the second you click "Get in as___"

I noticed the same with the Blackfoot. I have a joystick with a throttle lever which I use to control elevation. If I leave that in the up position, it's like holding down the Q button. I then get in the Blackfoot, and the rotors are already whirling away before I've even got both legs inside the cockpit.

And it looks a bit daft.

So to compare with the ticket about adding delayed starts to certain vehicles, I think that's a really good idea but at the very least should be inbuilt into vehicles so the engine cannot start until the getting-in animation has finished playing through.

Or maybe just say vehicles cannot start by simply pressing the movement buttons, and instead the player must go through the action menu to start the engine.

Exactly. The problem is exactly what you said in the first sentence. And I agree with the idea of using the action menu to start the engine before you are able to drive, though unfortunately many would hate this.

This shit with all land/water vehicles...
Here need to integrate engine launch process

Steps to reproduce:

1. Get on quadbike (engine off)
2. Select get out action
3. Immediately hold forward (while get out animation is playing)

Actual results:
Quadbike will turn on and move forward several meters while animation plays, then turns off.

Expected results:
Quadbike should stay put and ignore the movement input after "get out" has been selected.